1. Field of the Invention
The present invention relates to an image shifting module. More particularly, the present invention relates to an image shifting module for increasing image resolution.
2. Description of Related Art
Conventionally, a rear projection display device generates images by an optical engine, and projects the image on a screen. To enhance the resolution of the image projected on the screen, the display components employed in the optical engine should have higher resolution. However, since the display components having higher resolution are costly, a vibration mechanism is used to increase the image resolution in the conventional technology.
FIG. 1 is a schematic view of a structure of a conventional optical projection device. Referring to FIG. 1, the conventional optical projection device 100 includes an illumination system 110, a DMD 120, a projection lens 130 and a vibration mechanism 140. The illumination system 110 has a light source 112 for providing a light beam 114. The DMD 120 is disposed on the transmission path of light beam 114. The DMD 120 converts the light beam 114 into a plurality of sub-images 114a in each frame time. In addition, the projection lens 130 is disposed on the transmission path of the sub-images 114a, and the DMD 120 is disposed between the illumination system 110 and the projection lens 130. Moreover, the vibration mechanism 140 is disposed on the transmission path of the sub-images 114a and between the DMD 120 and the projection lens 130.
In the optical projection device 100 described above, the light beam 114 provided by the light source 112 passes through a color wheel 116, a light integration rod 117, a mirror set 118 and a total internal reflection prism (TIR prism) 119 sequentially. Thereafter, the TIR prism 119 reflects the light beam 114 to the DMD 120. At this moment, the DMD 120 converts the light beam 114 into a plurality of sub-images 114a, and the sub-images 114a pass through the TIR prism 119 and the vibration mechanism 140 sequentially. Then, the sub-images 214 are projected on the screen 400 via the projection lens 230.
Accordingly, when the sub-images 114a pass through the vibration mechanism 140, the vibration mechanism 140 changes the transmission path of some of the sub-images 114a at the same frame time. In other words, the sub-images 114a passing through the vibration mechanism 140 in some time of the same frame time are projected on a first position of the screen 400 (not shown). However, the sub-images 114 passing through the vibration mechanism 140 in other time of the same frame time are projected on a second position of the screen 400 (not shown). In general, the interval between the first position and the second position along the horizontal direction (X-axis) or vertical direction (Z-axis) is about ½ pixel. Since the conventional vibration mechanism 140 only shifts the image position of the sub-image 114a along the horizontal or vertical direction by ½ pixel, only the horizontal or vertical resolution may be increased.